1. Technical Field
The present disclosure relates to a lithium ion secondary battery.
2. Related Art
Electronics techniques have made remarkable advances in recent years. Portable electronic appliances have achieved reduction in size, weight, and thickness and increase in functionality. Along with this, the battery used as a power source of the electronic appliance has been strongly desired to have smaller size, weight, and thickness and higher reliability. In view of this, an all-solid lithium ion secondary battery including a solid electrolyte layer having a solid electrolyte has attracted attention.
In general, all-solid lithium ion secondary batteries are classified into two types of a thin-film type and a bulk type. The thin-film type is manufactured by a thin-film technique such as a PVD method or a sol-gel method. The bulk type is manufactured by powder compacting of an electrode active material or a sulfide-based solid electrolyte with low grain-boundary resistance. As for the thin-film type, it is difficult to increase the thickness of the active material layer and to increase the number of layers. This results in problems that the battery capacity is low and the manufacturing cost is high. On the other hand, the bulk type employs the sulfide-based solid electrolyte. In view of this, it is necessary to manufacture the battery in a glove box with a managed dew point. Moreover, it is difficult to make the solid electrolyte into sheet. Thus, decreasing the thickness of the solid electrolyte layer and increasing the number of layers of the battery have been an issue.
In view of the problem as above, Japanese Domestic Re-publication of PCT International Publication No. 07-135790 describes the all-solid battery manufactured by the industrially applicable manufacturing method that enables the mass production. In this manufacturing method, the oxide-based solid electrolyte, which is stable in the air, is used and the members made into sheets are stacked and then fired at the same time.
According to Japanese Patent No. 04745323, an object of the bulk type all-solid lithium ion secondary battery is to prevent the delamination (interlayer separation) and non-lamination (defect of non-attachment) caused by the difference in contraction ratio of the members and to reduce the manufacturing cost by reducing the firing temperature. In the disclosed example, the above object is achieved by adding a boron compound as the sintering aid. In the conventional method, however, problems remain that the lithium ion secondary battery has the high internal resistance and this results in the lower capacity.
In recent years, Japanese Patent No. 05193248 has disclosed the manufacture of the bulk type all-solid lithium ion secondary battery by the method in which the members are made into sheets and stacked and then fired at the same time. However, further reduction of the internal resistance and improvement of the capacity have been required.